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The Thermal Degradation Of Polymers Of N-butylcyanoacrylate Prepared Using Tertiary Phosphine And Amine Initiators
Published 1986 · Chemistry
Abstract The thermal degradation of polymers of n-butylcyanoacrylate, prepared using systems in which the propagating species is a macro-zwitterion, and of molecular weight from a few thousand to more than a million, have been examined by thermogravimetry, differential scanning calorimetry and pyrolysis-gas-liquid chromatography. In almost all cases quantitative conversion to monomer occurs and characterization of polymer thermally degraded to half its original mass shows that the molecular weight of the residual material is substantially the same as that of the original. The mechanism of degradation is considered to be chain unzipping with a zip length greater than the degree of polymerization of the longest chain examined; that is, 2350 units. The stability of the polymer has been found to vary with both the nature of the polymerization initiator and the chain length. This implies that the depolymerization process is end initiated at the residue of the polymerization initiator. Polymers having pyridinium chloride salt ends are significantly more stable than those having phosphonium or quaternary ammonium ends. Kinetically, the degradation of the phosphine initiated polymers is a simple first-order process, but that of the pyridine initiated polymers shows an induction period, followed by a period of acceleration before reaching first-order behaviour in the later stages. The higher stability of the pyridinium salt end may be associated with an internal rearrangement of the end group, as a consequence of which the polymer chain becomes a substituent of the pyridinium ring. Degradation mechanism is also influenced by the nature of the salt anion. Replacement of the chloride by sulphate causes the depolymerization reaction to be accompanied by charring, indicating that the sulphate ion is extracting the elements of water from the polymer.